High light transmittance in-plane switching liquid crystal display device

ABSTRACT

The present disclosure relates to a high light transmittance in-plane switching liquid crystal display device. The present disclosure suggests a horizontal electric field type liquid crystal display device comprising: a substrate; a plurality of gate lines disposed in horizontal direction on the substrate; a plurality of data lines disposed in vertical direction on the substrate; a plurality of pixel area defined by the crossing the plurality of the gate lines and the plurality of the data lines; a first pixel electrode having a plurality of segments arraying with a predetermined distance within the pixel area; a second pixel electrode having a plurality of segments arraying in parallel with the first pixel electrode within the pixel area; and a common electrode overlapping with the first pixel electrode and the second electrode within the pixel area.

This application claims the benefit of Korea Patent Application No.10-2010-0104590 filed on Oct. 26, 2010, which is incorporated herein byreference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a high light transmittance in-planeswitching liquid crystal display device. Especially, the presentdisclosure relates to a high light transmittance in-plane switchingliquid crystal display device in which all problems shown in thehorizontal electric field type liquid crystal display device, in whichthe pixel electrode and the common electrode are disposed in the samelevel plane, and the fringe filed type liquid crystal display device, inwhich the pixel electrode and the common electrode are overlapped, aresolved.

2. Discussion of the Related Art

The liquid crystal display device (or “LCD”) represents video data bycontrolling the light transmittance of the liquid crystal layer usingthe electric fields driven by thin film transistor (or “TFT”). Accordingto the direction of the electric field, the LCD can be classified in thetwo major types; one is vertical electric field type and the other isthe horizontal electric field type.

For the vertical electric field type LCD, the common electrode formed onthe upper substrate and the pixel electrode formed on the lowersubstrate are facing with each other for forming the electric field ofwhich direction is perpendicular to the substrate face. The twistednematic (TN) liquid crystal layer disposed between the upper substrateand the lower substrate is driven the vertical electric field. Thevertical electric field type LCD has merit of higher aperture ratio,while it has demerit of narrower view angle about 90 degree.

For the horizontal electric field type LCD, the common electrode and thepixel electrode are formed on the same substrate in parallel. The liquidcrystal layer disposed between the upper substrate and the lowersubstrate is driven in In-Plane-Switching (IPS) mode by the electricfield parallel to the substrate face. The horizontal electric field typeLCD has a merit of wider view angle over 170 degrees and faster responsespeed than the vertical electric field type LCD.

However, for the case of the horizontal electric field type LCD in whichthe pixel electrode and the common electrode are disposed on the samelevel plane, even though the horizontal electric filed is formed betweenthe pixel electrode and the common electrode, there is no electric fieldjust over the pixel electrode and the common electrode. Therefore, thearea occupied by the pixel electrode and the common electrode is to bethe non-transmittance area at which the liquid crystal is not driven.Consequently, even the pixel electrode and the common electrode is madeof a transparent material, they cannot contribute the transmittance areaand then the aperture ratio will be reduced by their area.

In order to above mentioned problem, the fringe field type LCD issuggested in which the common electrode corresponding to most of allportions of the pixel area is formed at under layer, and the pixelelectrode is formed upper layer by overlapping with the commonelectrode. In the fringe field type LCD, as the horizontal electricfield is formed over the pixel electrode, the high aperture ratio can beensured. However, the fringe field type LCD can ensure high apertureratio at only small area LCDs. When the LCD size is larger, theparasitic capacitance formed between the common electrode and the pixelelectrode is also increased. To solve this problem, the size of thetransistor should be getting larger and the gap between the pixelelectrodes will be narrower, so that the transmittance will be lowered.

SUMMARY OF THE INVENTION

In order to overcome the above mentioned drawbacks, the purpose of thepresent disclosure is to suggest a high light transmittance in-planeswitching liquid crystal display device in which the horizontal electricfield is formed at the space between the common electrode and the pixelelectrode and the space over the pixel electrode and the commonelectrode. Other purpose of the present disclosure is to suggest a highlight transmittance in-plane switching liquid crystal display device inwhich the parasitic capacitance formed between the common electrode andthe pixel electrode is reduced when the horizontal electric field isformed by the fringe electric field type LCD.

In order to accomplish the above purpose, the present disclosuresuggests a horizontal electric field type liquid crystal display devicecomprising: a substrate; a plurality of gate lines disposed inhorizontal direction on the substrate; a plurality of data linesdisposed in vertical direction on the substrate; a plurality of pixelarea defined by the crossing the plurality of the gate lines and theplurality of the data lines; a first pixel electrode having a pluralityof segments arraying with a predetermined distance within the pixelarea; a second pixel electrode having a plurality of segments arrayingin parallel with the first pixel electrode within the pixel area; and acommon electrode overlapping with the first pixel electrode and thesecond electrode within the pixel area.

The first pixel electrode and the second pixel electrode are formed onthe same level layer, and the common electrode is overlapping with thefirst pixel electrode and the second pixel electrode with having aninsulating layer therebetween.

The common electrode has a width which is 2˜3 times wider than any onewidth of the first pixel electrode and the second pixel electrode.

The first pixel electrode and the second pixel electrode are alternatelydisposed and being apart from each other with distance of 8 um˜10 um.

The common electrode configured to be supplied with a voltage of whichlevel is half of a maximum voltage difference between the pixelelectrode and the second pixel electrode.

The first pixel electrode and the second pixel electrode are configuredto have a voltage level difference having one value from 0V to 5Vtherebetween to form a horizontal electric field; and the commonelectrode, the first pixel electrode and the second pixel electrode areconfigured to have a voltage level difference having one value from 0Vto 2.5V between the common electrode and the first pixel electrode andbetween the common electrode and the second pixel electrode to form afringe field horizontal electric field.

The device further comprises a first thin film transistor formed at onecorner of the pixel area and connected to the first pixel electrode; anda second thin film transistor formed at another corner of the pixel areaand connected to the second pixel electrode.

The first thin film transistor is connected to a gate line disposed atone horizontal side of the pixel area and a first data line disposed ata first vertical side of the pixel area; and the second thin filmtransistor is connected to the gate line and a second data line disposedat a second vertical side of the pixel area.

The first thin film transistor includes a first gate electrode branchedfrom the gate line, a first source electrode branched from the firstdata line, and a first drain electrode facing with the first sourceelectrode; and the second thin film transistor includes a second gateelectrode branched from the gate line, a second source electrodebranched from the second data line, and a second drain electrode facingwith the second source electrode.

The first thin film transistor is connected to a first gate linedisposed at a first horizontal side of the pixel area, and a first dataline disposed at a first vertical side of the pixel area; and the secondthin film transistor is connected to a second gate line disposed at asecond side of the pixel area, and a second data line disposed at asecond vertical side of the pixel area.

The first thin film transistor includes a first gate electrode branchedfrom the first gate line, a first source electrode branched from thefirst data line, and a first drain electrode facing with the firstsource electrode; and the second thin film transistor includes a secondgate electrode branched from the second gate line, a second sourceelectrode branched from the second data line, and a second drainelectrode facing with the second source electrode.

The horizontal electric field type LCD according to the presentdisclosure includes a first pixel electrode and a second pixel electrodewhich are formed on the same level plane to form a first horizontalelectric field between them, and a common electrode formed under thefirst and second pixel electrodes to form a second electric fieldbetween the pixel electrode and the common electrode. As the horizontalelectric field is formed over the pixel electrode, the electrode areacan be used as the liquid crystal driving area so high lighttransmittance is ensured. Furthermore, as the overlapping area of thecommon electrode and the pixel electrode to form the horizontal electricfield over the pixel electrode can be minimized and the gap between thepixel electrodes is ensured to minimize the amount of the parasiticcapacitance. That is, as the in-plane switching type LCD according tothe present disclosure has the merits of the horizontal electric fieldtype LCD and the fringe field type LCD and overcomes the demerits ofthem, the present disclosure can suggest a high light transmittance LCDhaving lower driving power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is the plane view illustrating the structure of the high lighttransmittance in-plane switching liquid crystal display device accordingto the first embodiment of the present disclosure.

FIG. 2 is the cross-sectional view illustrating the structure of thehigh light transmittance in-plane switching liquid crystal displaydevice according to the first embodiment by cutting along the line I-I′.

FIG. 3 is the plane view illustrating the structure of the high lighttransmittance in-plane switching liquid crystal display device accordingto the second embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, referring to attached FIGS. 1 to 3, we will explainpreferred embodiments of the present disclosure. FIG. 1 is the planeview illustrating the structure of the high light transmittance in-planeswitching liquid crystal display device according to the firstembodiment of the present disclosure. FIG. 2 is the cross-sectional viewillustrating the structure of the high light transmittance in-planeswitching liquid crystal display device according to the firstembodiment by cutting along the line I-I′.

Referring to FIGS. 1 and 2, high light transmittance in-plane switchingLCD includes a plurality of pixel areas defined by a plurality of gatelines running to the horizontal direction over a transparent substrateSUB and a plurality of data lines running to the vertical direction overthe transparent substrate SUB which are crossing each other. A firstthin film transistor T1 is disposed at one corner of each pixel area,and a second thin film transistor T2 is disposed the other corner ofeach pixel area. The first thin film transistor T1 is connected to afirst pixel electrode PXL1 formed in the comb shape in which a pluralityof segments are disposed with a first predetermined gap within the pixelarea. The second thin film transistor T2 is also connected to a secondpixel electrode PXL2 formed in the comb shape in which a plurality ofsegments are disposed with a second predetermined gap within the pixelarea.

The first TFT T1 and the second TFT T2 are connected to the first gateelectrode G1 and the second gate electrode G2 which are branched fromthe same gate line GL, respectively. The first source electrode S1branched from the first data line DL1 is overlapped with one side of thefirst gate electrode G1. The first drain electrode D1 facing with thefirst source electrode S1 and being apart from the first sourceelectrode S1 with a predetermined distance is overlapped with the otherside of the first gate electrode G1. The first drain electrode D1 isconnected to the first pixel electrode PXL1. Even though it is not shownin figures, the first semiconductor layer is disposed between the firstgate electrode G1 and the first source-drain electrodes S1-D1 to playrole of channel layer.

Furthermore, the second source electrode S2 branched from the seconddata line DL2 is overlapped with one side of the second gate electrodeG2. The second drain electrode D2 facing with the second sourceelectrode S2 and being apart from the second source electrode S2 with apredetermined distance is overlapped with the other side of the secondgate electrode G2. The second drain electrode D2 is connected to thesecond pixel electrode PXL2. Even though it is not shown in figures, thesecond semiconductor layer is disposed between the second gate electrodeG2 and the second source-drain electrodes S2-D2 to play role of channellayer.

The first pixel electrode PXL1 and the second pixel electrode PXL2 havea comb shape in which a plurality of segments are disposed with apredetermined distance between them. Furthermore, each segments of thefirst pixel electrode PXL1 and the second pixel electrode PXL2 arealternately disposed each other. That is, one segment of the first pixelelectrode PXL1 and one segment of the second pixel electrode PXL2 areclosely disposed on the same level plane to form a horizontal electricfield therebetween.

When a scan signal is supplied to a gate line GL, the first TFT T1 andthe second TFT T2 turn on at the same time, and then the pixel signal issupplied to the first pixel electrode PXL1 and the second pixelelectrode PXL2 at the same time. In order to form a horizontal electricfield between the first pixel electrode PXL1 and the second pixelelectrode PXL2, they should have different voltage levels. For example,the first pixel electrode PXL1 preferably has the voltage range changingfrom 0V to 5V, while the second pixel electrode PXL2 preferably has thevoltage range changing from 5V to 0V, so that the voltage leveldifferent can be any one of from 0V to 5V. Consequently, it is possibleto drive the liquid crystal molecules with the horizontal electric filedformed between the first pixel electrode PXL1 and the second pixelelectrode PXL2, and to represent the video data.

With this structure, especially when the distance between the firstpixel electrode PXL1 and the second pixel electrode PXL2 is almost threetimes of the width of the pixel electrodes themselves PXL1 and PXL2, thehorizontal electric field is formed at the space between the pixelelectrodes PXL1 and PXL2, but there is no horizontal electric field justover the pixel electrodes themselves PXL1 and PXL2. Therefore, theliquid crystal molecules disposed over the pixel electrodes PXL1 andPXL2 cannot be driven. It is more preferable to make that the horizontalelectric field is formed over the pixel electrodes themselves PXL1 andPXL2.

To do so, in the first embodiment of the present disclosure, a commonelectrode COM is further included which is disposed under the pixelelectrodes PXL1 and PXL2 to be overlapped with them and has a widerwidth than the pixel electrodes PXL1 and PXL2. For example, the commonelectrode COM can be formed on the same level layer with the gate lineGL and the gate electrodes G1 and G2, and made of a transparentconductive material. Furthermore, a common line CL can be disposedparallel with the gate line GL for supplying the common voltage to thecommon electrode COM. The common electrode COM and the pixel electrodesPXL1 and PXL2 are overlapped each other with having the gate insulatinglayer GI and the passivation layer PAS therebetween.

Referring to FIG. 2 again, more detailed structure is explainedhereinafter. In order that the horizontal eclectic field is formed overthe pixel electrodes themselves PXL1 and PXL2, it is preferable that thecommon electrode COM has wider width than those of pixel electrodes PXL1and PXL2. As a result, a fringe field is formed between the surfaces ofthe pixel electrodes PXL1 and PXL2 and the edge of the common electrodeCOM. Due to this fringe field, the horizontal electric filed can beformed over the pixel electrodes PXL1 and PXL2. The width of the commonelectrode COM is preferably 2-3 times of the width of the pixelelectrodes PXL1 and PXL2. In other words, the edge of the commonelectrode COM is preferably protruded from the edges of the pixelelectrodes PXL1 and PXL2 with a length which is ½˜¾ times of the widthof the pixel electrodes PXL1 and PXL2. That is, it is preferable thatthe overlapped gap G of the common electrode COM and the pixel electrodePXL1 and PXL2 is ½˜¾ times of the width of the pixel electrodes PXL1 andPXL2.

In addition, when the horizontal electric field due to the fringe fieldis formed between the common electrode COM and the pixel electrodes PXL1and PXL2, the strength of the fringe field can be decided by consideringthe horizontal electric field formed between the first pixel electrodePXL1 and the second pixel electrode PXL2. For example, the commonelectrode COM can be supplied with the 2.5V level which is the middlelevel of the maximum difference voltage level between the first pixelelectrode PXL1 and the second pixel electrode PXL2.

The strength of the horizontal electric field formed between the firstpixel electrode PXL1 and the second pixel electrode PXL2 is defined bythe voltage difference between the voltage level of the first pixelelectrode PXL1 and the voltage level of the second pixel electrode PXL2.That is, the voltage difference between the first pixel electrode PXL1and the second pixel electrode PXL2 is any one value from 0V to 5V. Asthe common electrode has the constant voltage level of 2.5V, the fringefield having the voltage difference of any one from 0V to 2.5V is formedbetween the common electrode COM and the pixel electrodes PXL1 and PXL2.

Consequently, in the liquid crystal display device according to thefirst embodiment of the present disclosure, the horizontal electricfield is formed overall of the pixel area. Therefore, it is possible forthe present disclosure to suggest a high light transmittance in-planeswitching liquid crystal display device in which most of all area of thepixel region can be used as the light transmittance area.

Hereinafter, referring to FIG. 3, the second embodiment of the presentdisclosure will be explained. FIG. 3 is the plane view illustrating thestructure of the high light transmittance in-plane switching liquidcrystal display device according to the second embodiment of the presentdisclosure. The cross sectional structure of the horizontal electricfield type LCD according to the second embodiment is very similar withthat of the first embodiment. The difference is just on the arraying ofthe first TFT T1 and the second TFT T2.

Referring to FIG. 3, the high light transmittance in-plane switchingliquid crystal display device according to the second embodimentcomprises a plurality of pixel area defined by the crossing structure ofa plurality of gate lines running to the horizontal direction on atransparent substrate SUB and a plurality of data lines running to thevertical direction on the transparent substrate SUB. A first TFT T1 isdisposed at one corner of the pixel area, and a second TFT T2 isdisposed at another corner of the pixel area. The first TFT T1 isconnected to a first pixel electrode PXL1 formed as a comb shape in thepixel area. The second TFT T2 is connected to a second pixel electrodePXL2 formed as a comb shape in the pixel area.

The first TFT T1 is connected to a first gate electrode G1 branched froma first gate line GL1, and the second TFT T2 is connected to a secondgate electrode G2 branched from a second gate line GL2. In addition, afirst source electrode S1 branched from a first data line DL1 isoverlapped with one side of the first gate electrode G1. A first drainelectrode D1 facing with the first source electrode S1 and being apartfrom the first source electrode S1 with a predetermined distance isoverlapped with the other side of the first gate electrode G1. The firstdrain electrode D1 is connected to the first pixel electrode PXL1. Eventhough it is not shown in figures, a first semiconductor layer isdisposed between the first gate electrode G1 and the first source-drainelectrodes S1-D1, to play a role of channel.

Furthermore, the second source electrode S2 branched from the seconddata line DL2 is overlapped with one side of the second gate electrodeG2. The second drain electrode D2 facing with the second sourceelectrode S2 and being apart from the second source electrode S2 with apredetermined distance is overlapped with the other side of the secondgate electrode G2. The second drain electrode D2 is connected to thesecond pixel electrode PXL2. Even though it is not shown in figures, thesecond semiconductor layer is disposed between the second gate electrodeG2 and the second source-drain electrodes S2-D2 to play role of channellayer.

The first pixel electrode PXL1 and the second pixel electrode PXL2 havea comb shape in which a plurality of segments are disposed with apredetermined distance between them. Furthermore, each segments of thefirst pixel electrode PXL1 and the second pixel electrode PXL2 arealternately disposed each other. That is, one segment of the first pixelelectrode PXL1 and one segment of the second pixel electrode PXL2 areclosely disposed on the same level plane to form a horizontal electricfield therebetween.

In the second embodiment, the first TFT T1 turns on when the first gateline GL1 is selected, and the second TFT T2 turns on when the secondgate line GL2 is selected previously on the first gate line GL1.Therefore, there is time delay between when the first pixel electrodePXL1 is charged and when the second pixel electrode PXL2 is charged.However, during one picture frame is represented, the charged voltagesto each pixel electrodes PXL1 and PXL2 are maintained, so that ahorizontal electric field between the pixel electrodes PXL1 and PXL2 isformed.

As explained above, the difference between the first embodiment and thesecond embodiment is on the arraying structure of the thin filmtransistors T1 and T2 for forming the horizontal electric field betweenthe pixel electrodes PXL1 and PXL2, but there is no difference on thearraying structure of the commune electrode COM and the pixel electrodesPXL1 and PXL2. In the present disclosure, the main electric field fordriving the liquid crystal molecules is the horizontal electric fieldformed between the first pixel electrode PXL1 and the second pixelelectrode PXL2. The horizontal electric field due to the fringe fieldformed between the common electrode COM and the pixel electrodes PXL1and PXL2 contributes to drive the liquid crystal molecules disposed overthe pixel electrodes themselves PXL1 and PXL2. Consequently, accordingto the present disclosure, the horizontal electric field is formedoverall pixel area including the space just over the pixel electrodesPXL1 and PXL2.

Furthermore, the horizontal electric field due to the fringe field doesmake effect on the common electrode COM disposed just under its pixelelectrode not on the neighboring common electrode COM. Therefore, thereis a merit that it is possible to reduce the parasitic capacitancebetween the pixel electrode and the common electrode.

In addition, in the pixel area, as two pixel electrodes are drivingusing two thin film transistors, it is possible to make the drivingvoltage be lower. In other words, with the same driving voltage, it ispossible to design the pixel electrodes to be disposed with longerdistance. For example, the gap (A) between the pixel electrodes PXL1 andPXL2 can be 8˜10 um which is longer than 7 um used in conventional one.Actually, when the widths of the first pixel electrode PXL1 and thesecond pixel electrode PXL2 would be 2 um, the gap between the pixelelectrodes PXL1 and PXL2 would be 10 um, the width of the commonelectrode COM would be 4 um, and the gap between the common electrodesCOM would be 8 um, the light transmittance can be increased at least20%. Here, the gap (B) between the common electrodes COM is defined bythe gap (A) between the pixel electrodes PXL1 and PXL2 and theoverlapped area (G) between the common electrode COM and the pixelelectrodes PXL1 and PXL2.

While the embodiment of the present invention has been described indetail with reference to the drawings, it will be understood by thoseskilled in the art that the invention can be implemented in otherspecific forms without changing the technical spirit or essentialfeatures of the invention. Therefore, it should be noted that theforgoing embodiments are merely illustrative in all aspects and are notto be construed as limiting the invention. The scope of the invention isdefined by the appended claims rather than the detailed description ofthe invention. All changes or modifications or their equivalents madewithin the meanings and scope of the claims should be construed asfalling within the scope of the invention.

1. A horizontal electric field type liquid crystal display devicecomprising: a substrate; a plurality of gate lines disposed inhorizontal direction on the substrate; a plurality of data linesdisposed in vertical direction on the substrate; a plurality of pixelarea defined by the crossing the plurality of the gate lines and theplurality of the data lines; a first pixel electrode having a pluralityof segments arraying with a predetermined distance within the pixelarea; a second pixel electrode having a plurality of segments arrayingin parallel with the first pixel electrode within the pixel area; and acommon electrode overlapping with the first pixel electrode and thesecond electrode within the pixel area.
 2. The device according to theclaim 1, wherein the first pixel electrode and the second pixelelectrode are formed on the same level layer, and the common electrodeis overlapping with the first pixel electrode and the second pixelelectrode with having an insulating layer therebetween.
 3. The deviceaccording to the claim 1, wherein the common electrode has a width whichis 2˜3 times wider than any one width of the first pixel electrode andthe second pixel electrode.
 4. The device according to the claim 1,wherein the first pixel electrode and the second pixel electrode arealternately disposed and being apart from each other with distance of 8um˜10 um.
 5. The device according to the claim 1, wherein the commonelectrode configured to be supplied with a voltage of which level ishalf of a maximum voltage difference between the pixel electrode and thesecond pixel electrode.
 6. The device according to the claim 5, whereinthe first pixel electrode and the second pixel electrode are configuredto have a voltage level difference having one value from 0V to 5Vtherebetween to form a horizontal electric field; and wherein the commonelectrode, the first pixel electrode and the second pixel electrode areconfigured to have a voltage level difference having one value from 0Vto 2.5V between the common electrode and the first pixel electrode andbetween the common electrode and the second pixel electrode to form afringe field horizontal electric field.
 7. The device according to theclaim 1, further comprising: a first thin film transistor formed at onecorner of the pixel area and connected to the first pixel electrode; anda second thin film transistor formed at another corner of the pixel areaand connected to the second pixel electrode.
 8. The device according tothe claim 7, wherein the first thin film transistor is connected to agate line disposed at one horizontal side of the pixel area and a firstdata line disposed at a first vertical side of the pixel area; andwherein the second thin film transistor is connected to the gate lineand a second data line disposed at a second vertical side of the pixelarea.
 9. The device according to the claim 8, wherein the first thinfilm transistor includes a first gate electrode branched from the gateline, a first source electrode branched from the first data line, and afirst drain electrode facing with the first source electrode; andwherein the second thin film transistor includes a second gate electrodebranched from the gate line, a second source electrode branched from thesecond data line, and a second drain electrode facing with the secondsource electrode.
 10. The device according to the claim 7, wherein thefirst thin film transistor is connected to a first gate line disposed ata first horizontal side of the pixel area, and a first data linedisposed at a first vertical side of the pixel area; and wherein thesecond thin film transistor is connected to a second gate line disposedat a second side of the pixel area, and a second data line disposed at asecond vertical side of the pixel area.
 11. The device according to theclaim 10, wherein the first thin film transistor includes a first gateelectrode branched from the first gate line, a first source electrodebranched from the first data line, and a first drain electrode facingwith the first source electrode; and wherein the second thin filmtransistor includes a second gate electrode branched from the secondgate line, a second source electrode branched from the second data line,and a second drain electrode facing with the second source electrode.